(1) Field of the Invention
The present invention relates to a photoconductive toner. More particularly, the present invention relates to a photoconductive toner excellent in the photosensitivity.
(2) Description of the Prior Art
In the process where a reproduction image is formed without using a photosensitive drum or the like, use of a photoconductive toner has recently attracted attention. This photoconductive toner is prepared by dispersing or dissolving a photoconductive pigment and/or a charge transport substance in a binder resin and granulating the dispersion or solution by pulverization or spraying, and the toner per se has a photoconductivity.
As an example of the process for forming an image by using this photoconductive toner, there can be mentioned a process in which the steps of (i) uniformly applying the photoconductive toner on an electroconductive substrate to form a toner layer, (ii) uniformly charging the toner layer by corona discharge, (iii) subjecting the charged toner layer to imagewise light exposure, (iv) removing the toner in the exposed area from the substrate, (v) piling a copying sheet or the like on the toner layer and performing corona discharge from the back side of the transfer sheet to transfer the toner image and (vi) fixing the transferred toner image are sequentially carried out.
In this process, however, since the photosensitivity of the photoconductive toner is generally low, the difference of the charge between the exposed area and the non-exposed area is small in the latent image formed by the light exposure, and therefore, the contrast in the copied image is low.
As means for obviating this disadvantage, there has been proposed a method in which after formation of the toner image,corona charging is effected with the same polarity as that of the charge possessed by the toner, whereby the surface potential is increased to improve the photosensitivity. However, the above-mentioned problem cannot be completely solved.